The compound of formula (I): ##STR1## has two optically-active or "chiral" centers, i.e., at the 1' and 4' positions, each of which can exhibit an "R" or an "S" stereo configuration. As will be appreciated by those skilled in this art, a molecule of the compound of formula (I) exists as one of four possible isomers. Stereo configuration and the associated conventions of stereo chemistry are explained in essentially all standard texts on organic chemistry, for example, see March, J., Advanced Organic Chemistry, 3d. Ed., Chap 4, John Wiley & Sons, New York (1985).
In the compound of formula (I), there are two isomeric pairs each consisting of two enantiomers (isomers which are mirror images of each other). The isomeric paris are referred to as either "cis" (same side) or "trans" (opposite sides) with respect to the relationship of the non-hydrogen atoms attached to the chiral centers. The isomers may be named by prefixing the compound name with the absolute configuration of one of the chiral centers followed by the "cis" or "trans" designation, i.e., 1'R-cis, 1'R-trans, 1'S-cis and 1'S-trans.
The cis form of formula (I) is depicted below as formula (II): ##STR2## and is meant to represent both cis enantiomers. Thus, the convention of both the 1' and 4' bonds being bold faced is meant to include the enantiomers where the bonds are cis, whether out of the plane of the page or into it.
The racemic mixture (equal mixture) of the 1'R-cis and 1'S-cis enantiomers of the compound of formula (II) is known as carbovir or (.+-.)-carbovir. While racemic carbovir has been reported as having good activity against human immunodeficiency virus (HIV) associated with acquired immune deficiency syndrome (AIDS), the 1'R-cis enantiomer of carbovir, also known as (-)-carbovir, (hereinafter these terms are used interchangeably) has been found to have potent activity against this virus (see Vince, R., et al., Biochem. Biophys. Res. Commun., 156 (2), 1046 (1988)). In view of the high activity of the 1'R-cis enantiomer, it is particularly advantageous to have an efficient method for the synthesis of this enantiomer from relatively inexpensive starting materials.